Detailed microfacies analysis of carbonate rocks from the Tingri and Nyalam areas of southern Tibet allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes during the Early to Middle Jurassic. Based on texture, sedimentary structure, grain composition, and fossil content of ~. 500 thin sections, 17 microfacies overall were identified, and three evolutionary stages of sedimentary environments were defined. Stage 1 (Rhaetian?-lower Sinemurian Zhamure Formation) is characterized by siliciclastic and mixed siliciclastic-carbonate sedimentation on a barrier island environment. Stage 2 (upper Sinemurian-Pliensbachian Pupuga Formation) is characterized by high-energy grainstones with rich benthic faunas thriving on a carbonate platform, documenting transgressions in the early and late Pliensbachian. Stage 3 (Toarcian-lower Bajocian Nieniexiongla Formation) is characterized by low-energy mudstones intercalated with frequent storm layers on a carbonate ramp, documenting the climax of the early Toarcian transgression in the beginning of the unit. The transition from Stage 1 to Stage 2 points to a paleogeographic and paleoclimatic change, as the Tibetan Tethys Himalaya moved toward tropical latitudes characterized by highly suitable climatic and ecological conditions for carbonate sedimentation. The abrupt change from Stage 2 to Stage 3 is interpreted as a consequence of the early Toarcian Oceanic Anoxic Event, accompanied by short-term warming and sea-level rise. The failed recovery from the carbonate crisis in the early Bajocian, with continuing deposition on a low-energy carbonate ramp, may reflect tectonic migration toward higher southern latitudes and/or a reduction of the effect of warm tropical currents reaching the southern Tethys.
Han, Z., Hu, X., Li, J., Garzanti, E. (2016). Jurassic carbonate microfacies and relative sea-level changes in the Tethys Himalaya (southern Tibet). PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY, 456, 1-20 [10.1016/j.palaeo.2016.05.012].
Jurassic carbonate microfacies and relative sea-level changes in the Tethys Himalaya (southern Tibet)
Garzanti E.
2016
Abstract
Detailed microfacies analysis of carbonate rocks from the Tingri and Nyalam areas of southern Tibet allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes during the Early to Middle Jurassic. Based on texture, sedimentary structure, grain composition, and fossil content of ~. 500 thin sections, 17 microfacies overall were identified, and three evolutionary stages of sedimentary environments were defined. Stage 1 (Rhaetian?-lower Sinemurian Zhamure Formation) is characterized by siliciclastic and mixed siliciclastic-carbonate sedimentation on a barrier island environment. Stage 2 (upper Sinemurian-Pliensbachian Pupuga Formation) is characterized by high-energy grainstones with rich benthic faunas thriving on a carbonate platform, documenting transgressions in the early and late Pliensbachian. Stage 3 (Toarcian-lower Bajocian Nieniexiongla Formation) is characterized by low-energy mudstones intercalated with frequent storm layers on a carbonate ramp, documenting the climax of the early Toarcian transgression in the beginning of the unit. The transition from Stage 1 to Stage 2 points to a paleogeographic and paleoclimatic change, as the Tibetan Tethys Himalaya moved toward tropical latitudes characterized by highly suitable climatic and ecological conditions for carbonate sedimentation. The abrupt change from Stage 2 to Stage 3 is interpreted as a consequence of the early Toarcian Oceanic Anoxic Event, accompanied by short-term warming and sea-level rise. The failed recovery from the carbonate crisis in the early Bajocian, with continuing deposition on a low-energy carbonate ramp, may reflect tectonic migration toward higher southern latitudes and/or a reduction of the effect of warm tropical currents reaching the southern Tethys.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.